Most of the prior art antennas used for a plurality of frequencies in common had only one system feeding integrated antennas with signals and the signals of this one system were separated into different signal systems. This is because the integrated antennas themselves were so constructed that they were at a same potential both in DC and in high frequency (however distributions and phases are different in high frequency).
As described above, in the prior art antennas, there are many parts, in which antenna elements are used in common. In particular, an antenna for the frequency band for the car telephone is so constructed that it is included in an antenna for the AM/FM radio frequency band and that composite signals are obtained from the main body of the antenna through a feeder. Consequently, since it is impossible to separate signals in various frequency bands only by the main body of the antenna and it is necessary to integrate or mount externally a device such as a frequency separator apart from the main body of the antenna in order to separate different signals, it has a drawback that the cost is high.
Further, since a prior art antenna was constructed so as to include a car telephone frequency band antenna in the lower part and an AM/FM radio frequency band antenna in the whole, the body of the car had important influences particularly on the car telephone frequency band antenna, which had influences on the characteristics thereof.
Still further, since the prior art antenna has an inflexible construction, which cannot be deformed by an external force in the direction perpendicular to the antenna axis, it has a drawback that it is broken, when an external force exceeding the limit of strength of the construction material is applied thereto. This means that, in the case where it is mounted on a vehicle as a moving station, it is weak in vibration produced by the vehicle, vibration, shock, wind pressure and other external forces accompanied by the movement.
Other than the antenna used for a plurality of frequencies in common having only one signal in- and output system as described above, an antenna having two signal in- and output systems is disclosed e.g. in U.S. patent appplication Ser. No. 06/749,452, filed Jun. 27, 1985. This antenna is so constructed that a dipole portion (consisting of a sleeve and a radiator of 1/4.lambda.) constituting a car telephone frequency band antenna is mounted on a monopole portion constituting an AM/FM radio frequency band antenna so that they are insulated electrically and constructionally from each other so as to form 2 separate antennas. Consequently, since it has no portion used electrically in common in the antenna construction, it has a drawback that the constructional region occupied by the monopole section in the main body of the antenna is reduced and that as the result the reception efficiency is lowered.
Other similar prior art antennas are disclosed in U.S. Pat. Nos. 4,734,703 and 4,968,991. These antennas also have a car telephone antenna portion and an AM/FM antenna portion which are completely separate, and no portion is shared electrically. Therefore, they also involve the same problem, namely that the signal receiving efficiency of each antenna portion is low. In addition, separation of the respective antenna portions necessitates various circuits.